Alcohol use by youth and excessive alcohol use by adults are associated with multiple consequences. In terms of associations with alcohol, marijuana use is a risk factor for youth drinking, binge drinking, and crash fatalities involving alcohol. Therefore, the liberalization of marijuana policy among U.S. states may impact alcohol use, alcohol-related mortality, and the concurrent use of alcohol and marijuana. However, existing research about the impact of marijuana policies on alcohol use and related outcomes is limited and inconsistent, and has not accounted for the heterogeneity of marijuana policies, or fully accounted for the effect of alcohol policies. The objective of this proposal is to assess the impact of the liberalization of marijuana policies on individual-level alcohol use, concurrent and simultaneous use of alcohol and marijuana, and alcohol-related crash fatalities, suicides and homicides. We will address past research limitations by developing and testing a series of state- level marijuana policy measures that incorporate aspects of multiple marijuana policy domains (decriminalization, medical use, recreational use), and the policies and provisions within those domains. We will then select measures based on their ability to explain variance in marijuana use outcomes. The methods to develop marijuana policy measures will be similar to those used by our research team to successfully develop the `Alcohol Policy Scales'. The scales, which generated more valid predictions (based on goodness-of-fit) of alcohol-related outcomes compared with simpler measures, will be used in conjunction with the marijuana policy measures to fully account for both groups of policies in analyses. Our specific aims are to: Aim 1: a) Develop comprehensive measures of marijuana policies, and b) determine their relationships with marijuana use among youth and adults. Aim 2: a) Determine relationships between alcohol and marijuana policies across and within states over time; and b) assess how accounting for alcohol policies influences marijuana policy- marijuana use relationships. Aim 3: Determine relationships of marijuana policies with alcohol use measures and alcohol-related crash fatalities, suicide and homicide among youth and adults, while accounting for alcohol policies. We will examine: a) the independent effects of marijuana policies; and b) whether marijuana policies modify the relationships between alcohol policies and alcohol use and mortality outcomes. Aim 4: Assess how both alcohol and marijuana policies relate to the concurrent and simultaneous use of alcohol and marijuana, concurrent use disorder, treatment for concurrent use disorder, and crash fatalities involving both substances among youth and adults. Although we are interested in the effects of state-level policies, we will be examining individual-level outcomes with large population-based data sources including NSDUH, YRBS, FARS, and NVDRS from 1999-2018. The development of more comprehensive measures of the marijuana policy environment for use in conjunction with our measures of the alcohol policy environment is innovative, will overcome limitations of existing research, and will inform policy development and improve public health.